Next generation radar systems will be required to perform multiple missions and deliver higher levels of performance, while being readily integrated into their host platforms. Providing the ability for the radar system to operate in more than a single frequency band enables realizing optimum multi-mission performance. For example, lower operating frequencies generally provide superior long range surveillance capabilities particularly when the detrimental effects of weather are considered. In contrast, higher operating frequencies, with their associated narrower antenna beamwidths and wider available instantaneous bandwidth waveforms, excel for angular accuracy and target discrimination.
To support these multiple missions with high levels of operational flexibility and overall performance, next generation radars will also need to employ active phased array antenna systems. Phased arrays are configured from a multitude of individual radiating elements whose phase and amplitude states can be electronically controlled. The radiated energy from the collection of elements combines constructively (focused) so as to form a beam. The angular position of the beam is electronically redirected by controlling the elements' phases. Controlling both the elements' phases and amplitudes alters the shape of the beam. Each individual radiator of an active phased array antenna includes an initial low noise amplifier for receive mode and a final power amplifier for transmit mode, in addition to the phase and amplitude control circuitry.
Juxtaposing multiple single-band array antennas to achieve operation in more than a single frequency band is incompatible with platform limitations, particularly from a size viewpoint. Consequently, the multiple band coverage must be derived from a single antenna system. Previous attempts to do so have comprised performance. Phased arrays have been designed to provide operation on widely separating frequencies by using a common radiating element for the multiple bands. These designs exhibit low efficiencies at the lower operating frequency and lose full control of the beam at the upper frequency extreme. Most of these conventional phased arrays are also passive in that they do not include receive and transmit amplifiers with each radiating element.
Dual frequency active arrays have been demonstrated where the frequency bands are contiguous. The array radiating elements and their associated electronics attempt to cover the full frequency range. The drawback with these designs is that the amplifiers exhibit non-optimum performance due to their necessity to cover an extended bandwidth. Additionally, the quantity of elements and electronics is denser than what would generally be required for the lower frequency band, which leads to the array being heavier, having higher heat densities, and being too costly.
Most host platform limitations, especially mobile platforms, necessitate that the radar system be assembled with light weight, small volume components and structures. Highly reliable operation with ease of maintenance and component replacement is also required. In addition, the inclusion of active components will require an effective thermal management system, preferably using air to minimize cooling system power consumption and to maximize reliability. To date, no such radar systems are available.